This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to JP2001-154330 filed in Japan on May 3, 2001; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a non-lubricated wave gear device.
2. Related Art
A wave gear device usually includes a ring-shaped rigid internal gear, a flexible external gear that is shaped like a ring and is disposed on an inside of the rigid internal gear, and a wave generator that is fitted into an inside of the flexible external gear. The wave generator is composed of a rigid wave plug with an elliptical outline and a wave bearing that is fitted on an outer circumferential surface of the wave plug, so that the flexible external gear is flexed into an elliptical shape and the external teeth thereof that are positioned at both ends of the major axis of the elliptical shape engage the internal teeth of the rigid internal gear.
When the wave generator is rotated by a motor or the like, the engaging parts of both gears move in a circumferential direction. Since there is a difference in the number of teeth between the external teeth and the internal teeth, relative rotation occurs between the gears in accordance with the difference in the number of teeth. Typically, the difference in the number of teeth is two, and the rigid internal gear is fixed to a device housing or the like, so that a rotational output of significantly reduced speed is obtained from the flexible external gear based on the difference in the number of teeth.
In a wave gear device of the above structure, a lubricant is supplied to the engaging toothed parts of both gears, frictional sliding parts present between the external gear and the wave generator, and frictional sliding parts of the wave bearing of the wave generator. Examples of lubrication mechanisms for such parts are disclosed by JP-A 09-250609, JP-A 09-250610, and JP-A 09-250611.
However, depending on where the wave gear device is used, there are cases where lubricants cannot be used.
In cases where it is necessary to avoid environmental pollution, such as when the wave gear device is used in a clean room, or when the wave gear device is used in a vacuum, it is necessary to take measures, such as attaching a sealing mechanism, to stop the lubricant from leaking out to the periphery.
When the operating conditions of the wave gear device are severe, it is common for the contact surfaces of the external gear and the wave generator to be insufficiently lubricated. When these contact surfaces are insufficiently lubricated, a large thrust force operates on these contact surfaces, resulting in increases in the generation of heat and abrasion. This causes damage such as scorching.
Also, the agitating resistance of the lubricant that lubricates the frictional sliding parts of the wave bearing, which is attached to the outer circumference of the wave generator to allow relative rotation of the external gear and the wave generator, is high and is responsible for a large proportion of the power loss of the wave gear device.
An object of the present invention is to provide a wave gear device that is suited to use in environments where it is preferable not to use lubricants.
It is a second object of the present invention to provide a wave gear device where the frictional surfaces between the external gear and the wave generator can be sufficiently lubricated.
It is a third object of the present invention to provide a wave gear device that can avoid power loss due to agitating resistance of the lubricant used to lubricate the wave bearing of a wave generator.
In order to achieve the above and other objects, according to the present invention, there is provided a lightweight wave gear device, which comprises a ring-shaped rigid internal gear, a ring-shaped flexible external gear, and a wave generator for flexing the external gear in a radial direction to partially engage it with the internal gear, and for moving engaging parts of the internal gear and the external gear in a circumferential direction. The internal gear is made of a high-strength aluminum alloy or a copper alloy, and the external gear is made of structural steel or stainless steel. A plated coating of a hard material is formed on tooth surfaces of the internal gear by electroless plating, a DLC (Diamond Like Carbon) coating is laminated on a surface of the plated coating by a DLC coating process, and a DLC coating is formed on tooth surfaces of the external gear by a low-temperature DLC coating process.
Typically, the wave generator includes a rigid wave plug and a wave bearing that is fitted between an outer circumferential surface of the wave plug and an inner circumferential surface of the external gear. The wave bearing comprises a flexible outer ring whose outer circumferential surface contacts an inner circumferential surface of the external gear, an inner ring whose inner circumferential surface contacts an outer circumferential surface of the wave plug, and a plurality of rolling bodies that are inserted between the outer ring and the inner ring and are free to roll.
In this case, it is preferable for the outer ring of the wave generator to be made of SUJ2, stainless steel or beryllium copper. It is preferable that an inner circumferential surface of the external gear is formed with one of (i) an oxidized coating formed by a steam treatment, (ii) a DLC coating formed by a DLC coating process, (iii) an iron sulfide coating formed by a sulfurizing treatment, and (iv) an iron oxide coating formed by a steam treatment and a nitriding process. It is also preferable that the outer ring is formed on its outer circumferential surface with a DLC coating by a DLC coating process.
It is also preferable that the plurality of rolling bodies of the wave generator are made of a ceramic material, stainless steel or SUJ2. The inner ring of the wave generator is preferably made of SUJ2, stainless steel, beryllium copper, or ceramic material. While, it is preferable that a DLC coating by a DLC coating process is formed on a rolling surface portion in an inner circumferential surface of the outer ring, and that surfaces of the rolling bodies are formed with a DLC coating by a DLC coating process.
It is also preferable for the wave plug to be made of an aluminum alloy or a copper alloy.
In another aspect of the present invention, there is provided a wave gear device which has a ring-shaped rigid internal gear, a ring-shaped flexible external gear, and a wave generator that flexes the external gear in a radial direction and has the external gear partially engage the internal gear and that moves engaging parts of the internal gear and the external gear in a circumferential direction. In this wave gear device, the external gear is made of structural steel or stainless steel. The wave generator has a rigid wave plug and a wave bearing that is fitted between an outer circumferential surface of the wave plug and an inner circumferential surface of the external gear, wherein the wave bearing has a flexible outer ring whose outer circumferential surface contacts the inner circumferential surface of the external gear, an inner ring whose inner circumferential surface contacts the outer circumferential surface of the wave plug, and a plurality of rolling bodies that are inserted between the outer ring and the inner ring and are free to roll. The outer ring of the wave generator is made of SUJ2, stainless steel, or beryllium copper. The external gear has an inner circumferential surface formed with one of (i) an oxidized coating formed by a steam treatment, (ii) a DLC coating formed by a DLC coating process, (iii) an iron sulfide coating formed by a sulfurizing treatment, and (iv) an iron oxide coating formed by a steam treatment and a nitriding process. The outer ring has an outer circumferential surface formed with a DLC coating by a DLC coating process.
In yet another aspect of the present invention, there is provided a wave gear device which comprises a ring-shaped rigid internal gear, a ring-shaped flexible external gear, and a wave generator that flexes the external gear in a radial direction and has the external gear partially engage the internal gear, and that moves engaging parts of the internal gear and the external gear in a circumferential direction. In this wave gear device, the wave generator includes a rigid wave plug and a wave bearing that is fitted between an outer circumferential surface of the wave plug and an inner circumferential surface of the external gear. The wave bearing has a flexible outer ring whose outer circumferential surface contacts the inner circumferential surface of the external gear, an inner ring whose inner circumferential surface contacts the outer circumferential surface of the wave plug, and a plurality of rolling bodies that are inserted between the outer ring and the inner ring and are free to roll. The outer ring of the wave generator is made of SUJ2, stainless steel, or beryllium copper; the plurality of rolling bodies of the wave generator are made of a ceramic material, stainless steel, or SUJ2; and the inner ring of the wave generator is made of SUJ2, stainless steel, beryllium copper, or a ceramic material. A DLC coating is formed by a DLC coating process on a rolling surface portion formed in an inner circumferential surface of the outer ring; a DLC coating is formed by a DLC coating process on a rolling surface portion formed in an outer circumferential surface of the inner ring; and DLC coatings are formed by a DLC coating process on surfaces of the rolling bodies.
Here, it is preferable for the wave plug to be made of an aluminum alloy or a copper alloy.